In recent years, polylactic acid, polyglycolic acid, a copolymer of lactic acid and glycolic acid and like biodegradable and bioabsorbable polymers are applied to bone joining devices as substitute material for metals, ceramics etc. Since a bone joining material made up of such material is hydrolyzed and absorbed in vivo, there is no need after operation to remove the bone joining material by an additional operation, thereby advantageous. In contrast, a biodegradable and bioabsorbable bone joining device has drawbacks of low tensile strength and flexural strength in comparison with metals, ceramics and the like.
U.S. Pat. No. 4,898,186, U.S. Pat. No. 5,431,652, etc. propose to improve strength and maintenance of the polymer by molecular orientation of the polymer according to a variety of drawing techniques resulting in elevation of crystallinity thereof. Similarly, U.S. Pat. No. 4,743,257 proposes to use, as material thereof, the polymer whose functions are improved by blending a fibrous biodegradable and bioabsorbable polymer with the biodegradable and bioabsorbable polymer. However, further improvements in initial strength and maintenance of strength in vivo are requested.